Technology of tracking a target by associating the targets with one another among a plurality of cameras without a common viewing field is conventionally known. For example, spectral distribution information is acquired from image information acquired by imaging a subject with known color or spectral reflectivity placed in an imaging region for each camera. It is possible to associate the targets with one another among the cameras without depending on a light source environment by using the spectral distribution information acquired in this manner.
According to the conventional technology, it is required to prepare a subject with known color or spectral reflectivity, and it is further required that the subject is imaged by each camera and spectral distribution information is collected for each camera. Therefore, there is a problem that collecting the information is not easy when the number of cameras is large and tracking a target with high accuracy might be difficult.